The invention relates to a damper valve, particularly for an external steering damper or a hydraulic power steering of a motor vehicle, which includes a hydraulic positive displacement motor. The hydraulic positive displacement motor serves also as a steering damper by providing in the hydraulic connecting lines or passages extending between the motor and the servo-valve damper valves with throttling structures permitting fluid flow in at least one direction and including check valves which are arranged in parallel with the damper valves and are open in the opposite direction and have no or little throttling effect for fluid flows when they are in their open positions.
Such damper valves or rather power steerings which include such damper valves are known from DE 43 23 179 C1. The known damper valves include a valve support member in the form of a perforated plates, which have passages and which are either provided with resilient valve discs or a spring loaded valve plate by which hydraulic fluid flow through the passages can be controlled. The resilient valve discs on the front side of the perforated plate as well as the spring-loaded valve plate at the opposite side of the perforated disc are supported on the valve support member by bolts. The openings controlled in this arrangement by the resilient valve discs form throttling passages through which fluid can flow in one direction, whereas the openings controlled by the spring loaded valve plate serve as check valve structures which are open or only slightly throttling in the direction opposite to the one direction.
For a power steering with a double-acting piston cylinder unit each side of the unit is in communication with a motor connection of a servo valve so that a controllable pressure difference can be established between the two sides in one or the opposite direction. To insure the steering damper function, the connecting lines between the two sides of the piston-cylinder unit and the servo valve include the previously described damper valves in such an arrangement that their check valves open for a fluid flow into the piston cylinder unit.
External steering dampers are typically double acting piston cylinder units whose cylinder chambers are in communication with one another by way of throttling means in such a way that, upon movement of the piston, hydraulic fluid flows from one cylinder chamber to the other by overcoming a throttling resistance. Damper valves of the type as originally described can also be utilized with such steering dampers wherein in both piston stroke direction two damper valve arrangements in series must be provided between the cylinder chambers. The two serially arranged damper valves must be arranged with respect to fluid flow in opposition to one another in order to provide for equal damping effects in both direction of piston movement.
Each steering damper arrangement acts with respect to a steering control movement of the vehicle steering system as a control resistance--although of relatively small value. As a result, a return force occurring during vehicle operation because of a given steering kinematic, which tends to move the steering to a straight-ahead position can be affected more or less detrimentally. Consequently, a compromise must be made in the design of a steering damper arrangement such that, on one hand, there is a sufficient damper effect and, on the other hand, the return tendency of the steering mechanism during vehicle operation is not excessively affected.
It is the object of the present invention to provide an essentially improved design, which is capable of especially effectively dampening strong shocks acting on the steering mechanism.